Is this unique to Pennsylvania? One answer might be that they were born to diplomats or similar, but this is common to the USA as a whole, not just Pennsylvania. Might it be the Amish - do they not have US citizenship? Unlikely as just being born in the US gives you citizenship automatically except in the case of diplomats and other foreign government employees (spies perhaps!).

So it's not unique to Pennsylvania, and is (as far as this Brit is concerned) a somewhat obscure law that not many people would know about. Not only that, the question refers to people long dead. Foul, I cry, foul.

Maudibe, please ask a question only us Brits are likely to know the answer to!

That's not a question Brits can answer! We have an unwritten constitution so that doesn't help. It's assumed (or so it would seem) that anyone born in this country would be a British Citizen. You (if you wanted to become a British Citizen) could take am exam (after studying for it) that would enable you to become a citizen. It's often said that most (natural) British Citizens would fail it! Your system would seem better (did I just say that something American is better than the British version - I can't believe it!).

It's also complicated by Welsh, Scottish and Cornish people would like to be independent (well some of them anyway). Most Northern Irish wouldn't (for various reasons).

So here's a question - what is the official name of my country? No cheating by Googling it (like I did with your question!).

Just Googled citizenship myself, here's the answer:

lex soli: By birth in the UK to a parent who is a British citizen at the time of the birth, or to a parent who is settled in the UK
lex sanguinis: By birth abroad, which constitutes "by descent" if one of the parents is a British citizen otherwise than by descent (for example by birth, adoption, registration or naturalisation in the UK). British citizenship by descent is only transferable to one generation down from the parent who is a British citizen otherwise than by descent, if the child is born abroad.
By naturalisation
By registration
By adoption
But some of this is by fairly recent Act of Parliament (1980s).

Phew, I hadn't realised what a can of worms was going to be opened by your simple question!